Perfluoroalkylaldehyde



Patented June 15, 1954 PERFLUOROALKYLALDEHYDE ALKYLHEMIACETALS Donald R. Husted, St. Paul, and Arthur H. Ahlbrecht, White Bear Township, Ramsey County, Minn., assignors to Minnesota Mining & Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Application March 17, 1952, Serial N0. 277,084

3 Claims.

This invention relates to our discovery of a new and useful class of reactive fluorocarbon compounds.

These new compounds are the alkyl hemiacetals of fully fluorinated alkyl aldehydes, which may be termed the perfluoroalkyl aldehyde alkylhemiacetals, having the generic formula:

Rf OH In this formula the symbol R1 represents a saturated open-chain fluorocarbon group (normal or branched), consisting solely of carbon and fluorine, that is, a perfluoroalkyl group The symbol R represents a normal or branched hydrogen alkyl group (CinH2m+1").

The compounds of particular interest are the methyl, ethyl, propyl, butyl and amyl hemiacetals of the aldehydes which have from one to nine carbon atoms in the fluorocarbon group. For such compounds n has an integer value of 1 to 9, and m has an integer value of 1 to 5, in the above formula. The formula of these compounds can be written as:

where n and m have the values stated above.

The lower compounds are clear, colorless liquids. They are stable and can be distilled without decomposition. The higher compounds are solids. These compounds are all insoluble or only slightly soluble in water except as to the methylhemiacetal of trifluoroacetaldehyde,

CFsCI-HOH) (OCHz) i of carbon atoms of the hydrocarbon group (R), j

2 and the ratio thereof. The fluorocarbon group is both hydrophobic and oleophobic, whereas the hydrocarbon group is hydrophobic but oleophilic. Thus the solubility and surface active properties can be varied by varying these two disparate groups.

The hemiacetals which contain two or more (preferably three or more) carbon atoms in the fluorocarbon group have utility as plasticizers for fluorinated resins and polymers.

These new compounds are reactive and have value as chemical intermediates in the making of other compounds containing a fluorocarbon group.

These compounds have particular utility in providing a commercially valuable way of transporting the corresponding fluorocarbon aldehyde compounds in pure form. The fluorocarbon aldehyde compounds have the formula CnF2it+lCHO', or:

They are described and claimed in our Patent No. 2,568 .500 (Sept. 18, 1951). They are extremely reactive, readily polymerize, and are very sensitive to moisture, forming the corresponding monohydrates (aldehydrols) almost instantaneously in the presence of Water. Moreover, the lower aldehydes, having one to three carbon atoms in the fluorocarbon group, are gases or volatile liquids at room temperature. Thus trifiuoroacetaldehyde (GFSCHO) has a B. P. of about minus 15 (7., pentafluoropropionaldehyde has a B. P. of about 2 C., and heptafluorobutyraldehyde (CsFvCHO) has a B. P. of about 29 C'. For these reasons, it is diflicult to store and to ship the fluorocarbon aldehydes as such.

Moreover, it is difficult to prepare the fluorocarbon aldehydes in pure form free from the last traces of chloride when prepared by methods involving the presence of a chloride compound. The present compounds can be prepared and readily recovered in pure form from an intermediate reaction product mixture, without first isolating the aldehyde, in the practice of the manufacturing process wherein a fluorocarbon acid chloride compound is reduced by hydrogen in the presence of a palladium catalyst in ether solution to form a fluorocarbon aldehyde-hydrogen chloride-ether complex (see Example The 1owest member of the series, trifluoroacetaldehyde methylhcmiacetal,

CF3CH(OI-I) (OCHa) has a boiling point of about 96 C. at 740 mm. pressure. It is soluble in water and rapidly reacts with evolution of heat, yielding an oily or semi-solid product that is believed to be the aldehyde monohydrate, trifiuoroacetaldehydrol,

The higher compounds which contain two or more carbon atoms in the fluorocarbon group or in the hydrocarbon group (and which thus have a total of four or more carbon atoms in the molecule) are insoluble or only slightly soluble in water, and have boiling points of at least about 100 C. They are stable compounds and can be conveniently stored and shipped. The corresponding fluorocarbon aldehyde compound can be recovered whenever desired by distillation from a mixture of the hemiacetal compound and sulfuric acid or other appropriate dehydrating agent. Thus trifluoroacetaldehyde, CFsCI-IO, can be distilled from a mixture of sulfuric acid and CF3CH(OI-I) (OCH3) In some cases it will not be necessary to recover the aldehyde compound as such, since it can react as fast as released to form an aldehyde derivative compound, as in the case of reactions performed in sulfuric acid as the reaction medi- When the present compounds are employed as a means of transporting the perfluoropropionaldehyde and higher aldehyde compounds, being converted to the latter at the timeof use, the methyl compounds will be preferred in order to minimize cost. These can be represented by the formula: CnF2n+lCH(OH)(OCH3), where n has a value of 2 or more. However, in the caseof the liemiacetals of trifiuoroacetaldehyde, the ethyl compound, CFaCI-UOH) (OC2F5), is preferred owing to the water solubility of the methyl compound.

The reaction properties of the present compounds do not parallel those of the corresponding analogs of the hydrocarbon system of conventional organic chemistry. For example, the fluorocarbon aldehyde hemiacetals are not easily converted to the full acetals:

where R and R" stand for alkyl groups that are the same or different. In fact we have not yet succeeded in making this conversion. The corresponding hydrocarbon aldehyde acetal compounds: CnH2n+1CH(OR') (OR") are easily formed from the hemiacetals. The hydrocarbon aldehyde hemiacetals are easily converted to the aldehyde cyanohydrins by the action of hydrogen cyanide. When we attempted this reaction with the fluorocarbon aldehyde hemiacetals, the starting material was recovered unchanged. We found it necessary to react hydrogen cyanide with the fluorocarbon aldehyde itself, in an anhydrous ether solvent vehicle at a reduced temperature, to obtain the cyanohydrin, which could be recovered by distillation. Thus in this way we were able to make heptafluorobutyraldehyde cyanohydrin, C3F7CH(OI-I)(CN), B. P. 62.5-64 C. at 3 mm., M. P. in neighborhood of 70-100 C.,

from heptafluorobutyraldehyde, CsFvCI-IO; but we were unable to make it from a hemiacetal compound. These points demonstrate the greater stability of the fluorocarbon hemiacetal compounds.

The following examples serve to illustrate the preparation of the subject compounds.

Erwmple 1 'Dry Ice-acetone bath. It was charged with 3 ml. (0.03 mole) of trifluoroacetaldehyde (CFsCHO) Then 1 ml. (0.031 mole) of anhydrous methyl alcohol (CH3OH) was added dropwise with cooling and shaking. The reaction mixture was allowed to warm to room temperature and was then distilled through a semimicro fractionating was 1.241.

column.

The fraction distilling at 96-96.5- C. at 729 mm. pressure was recovered and was identified as relatively pure trifluoroacetaldehyde methylhemiacetal, CF3CH(OH) (OCI-Iz). It had a refractive index at 25 C. of 1.3259. It is a colorless liquid. Analysis showed 28.0% C. and 41.0% F., in good agreement with the calculated values of 27.7% C. and 43.8% F. As previously mentioned, this compound is soluble in water and rapidly reacts therewith.

Example 2 In a similar manner trifluoroacetaldehyde (CFSCHO) was reacted with anhydrous ethyl alcohol (C2H5OH) and the reaction mixture was distilled to obtain a 76.5% yield of trifiuoroacetaldehyde ethylhemiacetal,

a colorless liquid having a boiling point of 104- 105 C. at 746 mm. pressure. The refractive index at 25 C. was 1.3408 and the density at 20 C. Unlike the methylhemiacetal, this compound was found to be insoluble in water.

Example 3 C2F5CI-I(OH) (OCzFs) The refractive index at 20 C. was 1.3302.

Example 4 The equipment was like that in Example 1 but a 50 ml. flask was used. The flask was charged with 2.64 grams (0.057 mole) of anhydrous ethyl alcohol. Then 11.4 grams (0.057 mole) of hep tafiuorobutyraldehyde, CsFtCHO, was added dropwise with shaking. The flask was removed from the cooling bath and allowed to stand for 1 hour. The reaction mixture was distilled through a semimicro distilling column.

The fraction distilling at 106-1065 C. at 747 mm. was recovered in a yield of 9.7 grams and was identified as relatively pure heptafiuorobutyraldehyde ethylhemiacetal,

CsFvCH (OH) (OCzHs) It was a colorless liquid and had a density at 20 C. of 1.411, and a refractive index at 20 C. of 1.3245. The hydrolysis equivalent was 246 (theor. 244). Analysis showed 7.4% H, 30.4% C. and 52.1% F., in good agreement with the values calculated from the formula, namely, 6.97% OH, 29.5% C. and 54.5% F.

The recovery of the corresponding aldehyde is illustrated by the following experiment:

In a 200 ml., 2-necked flask, fitted with a dropping i'unnel and a distillation head, condenser, and receiver vented through a Dry Ice-acetone cooled trap, was placed 80 grams (0.402 mole) of heptafluorobutyraldehyde ethylhemiacetal,

Through the dropping funnel was slowly added 80 grams (0.765 mole) of concentrated sulfuric acid. The mixture was shaken to insure mixing and was then distilled. The heptafluorobutyraldehyde product, C'sFqCHO. was recovered as the fraction distilling at 29 C., in a yield of 90%.

Example This example illustrates the direct preparation of the present compounds from reaction mixtures containing fluorocarbon aldehyde-hydrogen chloride-ether complexes as obtained from the Rosenmund procedure, without the necessity of first recovering the aldehyde in free form as an intermediate. (The preparation of these complexes is described in detail in our copending application Serial No. 212,516, filed on February 23, 1951.)

The apparatus consisted of a dry 250 ml. 3- necked flask equipped with a stirrer, a gas inlet tube extending below the liquid surface, and a. reflux condenser cooled by a Dry Ice-acetone mixture (condensers Nos. 6428 and 6429 manufactured by the Scientific Glass Company, Bloomfield, N. J are exemplary).

The flask was charged with 80 ml. of dry diethyl ether, 23.2 grams (0.1 mole) of heptafiuorobutyryl chloride (C3F7COC1), 2 grams of charcoal-supported palladium catalyst (5% palladium). and 6 drops of quinoline-S catalyst-regulator. (This regulator serves to poison the palladium catalyst so as to inactivate it towards reduction of the desired aldehyde product; it can be made by refluxing sulfur in quinoline.) Hydrogen was passed in slowly with vigorous stirring for a period of 10 hours at the reflux temperature of the ether.

The resultant reaction product mixture com A tained the fluorocarbon aldehyde reduction product bound in a complex with I-ICl and ether:

CsFiCHO HCI- CzHaOCaHs This complex is stable and distillable. It can be broken with water to form the monohydrate of the aldehyde, from which the aldehyde can be recovered by distilling in the presence of concentrated sulfuric acid. However, the aldehyde product contains traces of H01 which can only be eliminated with difiiculty.

In the present work, the reaction product mixture was filtered to recover the catalyst and the filtrate was distilled. The fraction distilling at 52-53 C. at 740 mm. contained the aldehyde- I-ICl-ether complex together with about 5% of impurities.

18 grams of this product was placed in a 50 ml. flask cooled by an ice bath and fitted with a dropping funnel and a reflux condenser cooled by Dry Ice-acetone. Then 2.5 m1. of anhydrous ethyl alcohol was added dropwise. The resultant product was fractionally distilled. The fraction boiling at 104-106 C. at 742 mm. was recovered and provided 11.5 grams yield) of heptafluorobutyraldehyde ethylhemiacetal.

CsF7CH(OI-I) (OC2H5) Example 6 In a similar manner an aldehye-HCl-ether complex was obtained by reduction of heptafluorobutyryl chloride (CaFqCOCl) and this was reacted with anhydrous methyl alcohol and the product distilled to obtain a fraction identified as heptafiuorobutyraldehyde methylhemiacetal, C3F7CH(OH) (OCI-Is) a colorless liquid having a boiling point of 97-100 C. at '755 mm. The refractive index at 25 C. was 1.3140.

The above procedure can be simplified by adding the alcohol to the original reaction product mixture containing the aldehyde-HCl-ether complex, omitting the intermediate filtration and fractionation. The hemiacetal end product can then be recovered by fractional distillation.

We claim:

1. As new compounds, the perfluoroalkyl aldehyde alkylhemiacetals having the formula:

where n has an integer value of 1 to 9 and m has an integer value of 1 to 5.

2. The compounds of claim 1 which have at least four carbon atoms in the molecule.

3. The compounds of claim 1 which have at least five carbon atoms in the molecule and at least three carbon atoms in the fluorocarbon group (CnF2n+1).

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,433,844 Hanford Jan. 6, 1948 2,468,861 Bridge et al May 3, 1949 

1. AS NEW COMPOUNDS, THE PERFLUOROALKYL ALDEHYDE ALKYLHEMIACETALS HAVING THE FORMULA: 